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| United States Patent |
5,061,557
|
|
Kot
, et al.
|
October 29, 1991
|
Reinforced composite structure
Abstract
One or more plies of reinforced elastomer, particularly two plies (10),(12)
of rubber reinforced with twisted filament metallic cords (14) and more
particularly a tire belt made up of the two plies (10),(12) is disclosed
having cords (14) of 2x.30HT construction with opposed 23.degree. angles
to the direction of reinforcement of the belt.
| Inventors:
|
Kot; Kenneth M. (Akron, OH);
Lee; Byung-Lip (Akron, OH)
|
| Assignee:
|
The Goodyear Tire & Rubber Company (Akron, OH)
|
| Appl. No.:
|
362626 |
| Filed:
|
June 6, 1989 |
| Current U.S. Class: |
428/295.7; 57/213; 57/217; 57/218; 57/236; 57/237; 57/238; 57/902; 152/527; 428/105; 428/297.1 |
| Intern'l Class: |
B32B 005/12 |
| Field of Search: |
428/105,114,294,295
57/218,213,217,236,237,238,902
|
References Cited
| Foreign Patent Documents |
| 43171/72 | Jun., 1972 | AU.
| |
| 20904/83 | Nov., 1983 | AU.
| |
| 24062/84 | Nov., 1984 | AU.
| |
| A157716 | Oct., 1985 | EP.
| |
| 103093 | Dec., 1981 | JP.
| |
Primary Examiner: Bell; James J.
Attorney, Agent or Firm: Lewandowski; T. P.
Parent Case Text
This is a division of application Ser. No. 133,169, filed Dec. 11, 1987,
which is a continuation of application Ser. No. 836,934, filed Mar. 6,
1986, now abandoned.
Claims
What is claimed is:
1. A reinforced ply of elastomer having a cord of two twisted filaments
each filament of less than 0.34 millimeters diameter made from steel with
a carbon content by weight of 0.7 to 0.90 percent, said ply having at
least 8.66 cords per centimeter spaced in a direction lateral to the
direction of reinforcement of the ply.
2. The reinforced ply defined in claim 1 wherein said cord diameter has a
range of 0.25 to 0.68 millimeters.
3. The reinforced ply defined in claim 1 wherein said cord has a lay length
of 20 to 100 times the filament diameter.
4. The reinforced ply defined in claim 1 wherein the lay length of said
cord is 10 to 16 millimeters.
5. A reinforced composite structure comprising an elastomeric body, a
plurality of individual, twisted filament reinforcing cords of a diameter
from 0.25 to 0.68 millimeters, said cords being laterally spaced at 8.66
to 11.02 cords per centimeter in said body and said body having a modulus
greater than 120 MPa.
6. The reinforced composite structure defined in claim 5 wherein each said
cord has a lay length of 20 to 100 times the filament diameter.
7. The reinforced composite structure defined in claim 5 wherein said cords
are comprised of two single filaments.
8. The reinforced composite structure defined in claims 5 or 7 wherein said
filaments have a diameter of less than 0.34 millimeters.
9. The reinforced composite structure of claims 5 or 6 wherein the lay
length of said cord is 14 millimeters.
10. A reinforced composite structure comprising an elastomeric body, a
plurality of individual, twisted filament reinforcing cords, said cords
having a Tabor stiffness of less than 60 grams, said ply having a critical
load greater than 19.8 MPa and a critical strain not exceeding 11.0
percent.
11. The reinforced composite structure defined in claim 10 wherein the
critical load range is from 19.8 to 23.8 MPa.
12. The reinforced composite structure defined in claim 10 wherein the
critical strain range is from 9.0 to 11.0 percent.
13. A reinforced composite structure comprising an elastomeric body, a
plurality of individual, twisted filament reinforcing cords, said cords
having a Tabor stiffness of less than 60 grams and a modulus greater than
190 GPa and a filament diameter less than 0.34 mm.
14. The reinforced composite structure defined in claim 13 wherein the
cords have a diameter of less than 0.68 mm.
15. A reinforced composite structure comprising an elastomeric body, a
plurality of individual, twisted filament reinforcing cords, said cords
having a fialment diameter of less than 0.34 mm and a cord modulus greater
than 190 GPa and said ply capable of 2,000,000 or more cycles at a maximum
load of 16.9 MPa and a frequency of 10 cycles/sec.
16. A reinforced composite structure comprising an elastomeric body, cords
of two twisted filaments, said cords spaced parallel to each other in a
plane forming the structure with a ratio of actual to nominal rivet of
1.94 between points on the cords which are a quarter lay length apart
along the length of the cords and capable of satisfactory rubber-cord
adhesion at a nominal rivet of 0.53 times the cord diameter.
17. The reinforced ply and structure defined in claims 1, 5, 10 or 16
wherein said cords have an average flare length of 8 mm one minute after
cutting the ends thereof.
Description
The present application relates to a composite laminate structure of cord
reinforced elastomer and more particularly to a cord reinforced composite
having rubber where preferably the cord is metallic. Even more
particularly, the structure is for tires and preferably a tire belt
wherein at least one of two plies in the belt has the cords therein biased
with respect to the direction of rotation of the tire.
Reinforced elastomeric articles are well known in the art for example for
conveyor or like type belts, tires etc., with cords of textile and/or fine
steel wire, particularly belts for pneumatic tires with up to four plies
with the cord reinforcement between adjacent plies being opposingly biased
with respect to the direction of movement of the tire where it is desired
to reinforce in the lateral direction in addition to the direction of
rotation of the tire. Further, cords made of multi twisted filaments of
fine wire with two or more filaments in a single strand construction
having a wrap filament therearound to reinforce the above structure have
also long been known. More recently multi strand cords such as 2+7x.22+1
have been found necessary to meet the higher demand of fatigue life for
composites in tire belts but are more expensive to make. Most recently,
there has been use of single strand cords of multi filaments which are not
twisted about each other but rather twisted altogether as a bundle or
bunch to simplify the cord construction. Higher fatigue life requirements
for composites in tires have resulted in cords with smaller filament
diameter requiring more filaments in the cord to obtain the necessary
strength.
Many problems have arisen particularly with respect to bonding a ply with
an opposing angle of reinforcement to an adjacent ply to form a composite
laminate. For example when the above composite laminate has a flexible
rubber matrix as in a tire belt and is loaded by a uniform tensile stress
resulting from both tire inflation and footprint load, the oppositely
directed in-plane shear stresses in each ply result in a large strain
gradiant near each edge of the laminate as indicated in FIG. 1.
Consequently under tension the cord rubber composite belt is highly
susceptible to initiation of interply shear fracture near the edge of the
belt which is known as belt edge separation. Under both static and cyclic
loading, the belt edge separation is initiated by cracking around the
individual cord ends at the cord-rubber interface of the plies. The load
for initiation of belt edge separation constitutes a threshold level for
semi-infinite fatigue life of cord-rubber composites. When the maximum
stress during cyclic loading does not exceed the initiating load for belt
edge separation, the cord rubber composites exhibit no damage and
therefore virtually infinite fatigue life. The load at which the composite
fails in delamination measures the load, referred to below as gross load,
carrying capability of the composite structure which is dependent upon
three factors assuming adequate cord to rubber adhesion. The factors are
cord modulus, the ratio of cord volume to rubber volume which is often
expressed as the number of cord ends per inch, and the angle of cord
reinforcement. As the angle of cord reinforcement approaches the direction
of rotation of the tire the support from the reinforcement in the lateral
direction moves toward zero. An increase in the above-mentioned two other
cord related factors generally results in an increase of weight for the
belt. Added weight means added cost and higher rolling resistance of a
tire. Lighter cords with a lower modulus do not solve the problem because
even though they have lower weight they also have a lower cord modulus
which must be offset by increasing the ratio of cord to rubber volume.
This increase in cord volume is limited by the physical size of the cord
and the resulting spacing between the cords which governs the ability of
the rubber to penetrate between the cords for good cord to rubber
adhesion.
As indicated below the present invention will be shown to have
substantially improved the critical load for preventing belt edge
separation without decrease of the load carrying capability of the overall
tire belt over conventional belt constructions typically reinforced by
2+2x.25 and 2+7x.22+1 cord constructions.
A reinforced composite structure according to the present invention is
preferably a reinforced ply of elastomer for tire belts having two layers
of cord, each cord made of two single 0.30 mm diameter filaments, said
filaments made from steel with a carbon content by weight of 0.82%, each
layer having 9.45 cords per centimeter laterally spaced in a direction
lateral to the direction of the width of the tire at angles of 23.degree.
to the direction of movement of the tire and opposed to each other. Also
included is a reinforced ply of elastomer for tires having a cord of two
twisted filaments, each filament of less than 0.34 mm diameter made from
steel with a carbon content by weight of 0.7 to 0.9%, said ply having at
least 8.66 cords per centimeter spaced in a direction lateral to the
direction of reinforcement of the ply. Further, the reinforced composite
structure can comprise an elastomeric body, a plurality of individual
twisted filament reinforcing cords of a diameter from 0.25 to 0.68 mm, the
cords being laterally spaced at 8.66 to 11.02 cords per centimeter in the
body and the body having a modulus greater than 120 MPa psi.
A composite envisioned as an invention hereof can be an elastomer body, a
plurality of individual, twisted filament reinforcing cords, the cords
having a Tabor stiffness of less than 60 grams, the ply having a critical
load separation greater than 19.8 MPa with critical strain not exceeding
11.0%. Also envisioned is an elastomeric body, a plurality of individual,
twisted filament reinforcing cords, the cords having a Tabor stiffness of
less than 60 grams, and a modulus greater than 190 GPa and a filament
diameter of less than 0.34 mm. Finally, a composite according to the
present invention is envisioned as an elastomeric body, a plurality of
individual, twisted filament reinforcing cords, the cord filaments having
a diameter of less than 0.34 mm and a cord modulus greater than 190 GPa,
the ply having a fatigue life to withstand no damage at 2,000,000 cycles
when loaded up to 16.9 MPa and cycled at 10 cycles per second.
The above composites have the advantages of a 20% increase in critical load
over a comparable composite reinforced with 2+2x.25 cord. A smaller
diameter of the cord of the reinforcement of the present invention results
in less rubber gauge being used where a comparable thickness of rubber is
laid on each side of the reinforcing cord upon calendering. Where two
filament cord is used the result is an open cord having no core resulting
in better rubber penetration. The two filament cord results in a cost
savings over cords of three filaments or more in the manufacture of the
cord. A smaller diameter cord results in less weight in the reinforcement
resulting in lower rolling resistance for a tire thereby reinforced. A
tire belt reinforced with a two filament cord having filament diameters of
0.30 mm results in 1 to 2% better rolling resistance compared to the same
system reinforced with 2+2x.25 cord. Similarly, the above two filament
cord results in a 15% or better plunger energy for tires over 2+2x.25 cord
for comparable reinforcements. Use of a two filament cord having filament
diameters of 0.30 mm and made of high tensile steel results in a 16%
increase in the composite modulus without effecting the composite strain
which remains the same in comparison to 2+2x.25 conventional steel cord at
7.87 ends per centimeter where the end count for the two filament cord is
increased to 9.45 ends per centimeter. Finally, the above two filament
cord results in a 2 to 6% greater composite stiffness over 2+2x.25 cord
reinforced composites in tire belts even though the diameter of the two
filament cord is smaller and its weight has been reduced over 2+2x.25 cord
.
The above advantages of the invention will become readily apparent to one
skilled in the art from reading the following detailed description of an
embodiment of the invention when considered in the light of the
accompanying drawings in which
FIG. 1 illustrates schematically a composite of cord and rubber in a loaded
and unloaded condition;
FIG. 2 illustrates a perspective of a portion of a tire having parts cut
away to illustrate a belt package having composite structures according to
the present invention; and
FIGS. 3 and 4 are cross sections through cords in accordance with an
embodiment of the present invention at points one quarter lay length apart
from each other in the cords.
Referring to FIGS. 1 and 2 of the drawings a single ply is illustrated in
an unloaded condition, shown dotted, and in a loaded condition under
tension indicated by the arrows F. This ply is shown in FIG. 2 within a
pneumatic tire with a radial carcass and a second ply 12 forming the belt
package for the tire. Both plies are reinforced with cords 14 spaced
laterally to the direction of reinforcement indicated by arrows F and
preferably at an angle of 23.degree. but with the cord angles of the two
plies 10 and 12 opposing each other. Angles of 18.degree. to 28.degree.
for reinforcing cords are found useful.
The cords are surrounded by an elastomer preferably rubber and the
cord-rubber composite structure forms the plies 10 and 12. The plies 10
and 12 in turn form a laminate structure such as the belt reinforcement
for the tire illustrated in FIG. 2. It will be appreciated that other
laminates can be formed using principals of the present invention for
reinforcing other articles such as industrial belts and that a single ply
of the present invention can be used with known or conventional plies to
also form new useful reinforced composite structures.
Preferably the cords 14 are comprised of two filaments of finely drawn high
tensile steel wire twisted about each other. Preferably the filament
diameter is 0.30 mm and its tensile elastic modulus is 190 GPa or greater.
The cord has a uniform lay length of 10 to 16 mm and in the preferred
embodiment 14 mm.
The cord of the preferred embodiment will be designated as 2x.30HT
designating a two filament twisted cord having filaments of 0.30 mm
diameter of a high tensile steel wire wherein high tensile is steel made
with a carbon content by weight of 0.7 to 0.9% and preferably 0.82%.
Referring to FIGS. 3 and 4 if a cross section is taken through a ply at
right angles to the cords 14 they would appear as illustrated in FIG. 3
wherein d is the diameter of the cord defined by the circle inscribing the
two filaments, being 0.60 mm in the preferred embodiment. Conventionally
the inscribed diameter of the cord is used to define the rivet illustrated
by the space designated in FIG. 3 which is a function of the spacing of
the cords laterally across the ply. While this definition of the rivet,
being a nominal one, is correct for the cross section of the cord at one
point as is illustrated in FIG. 4, the actual rivet h at a point a quarter
a lay length down the length of the cord from that point illustrated in
FIG. 3 is quite different. For a tightly twisted two filament cord as
illustrated in the preferred embodiment the ratio of the actual to nominal
rivet h,r approaches 2 to 1 between the point in FIG. 4 and that in FIG. 3
as nominal rivet approaches zero. This high ratio of actual to nominal
rivet over the length of the two filament cord permits closer lateral
spacing of the cord in the ply over conventional and larger diameter cords
such as 2+7x.22+1 and 2+2x.25.
The limit of how many cords can be placed in a rubber body to reinforce it
is determined by the minimum rivet allowable for proper adhesion of rubber
to cord. For 2+2x.25 cord this limit is 7.87 ends per centimeter while for
2+7x.22 wire it is 6.30 ends per centimeter the end count dropping as the
diameter of the wire increases as illustrated in Table 1 below.
TABLE 1
______________________________________
Tensile Stress-Strain Properties
of `Belt` Composites
Reinforce-
ment 2 + 7X.22 + 1
2 + 2X.25 2 + 2X.25
2X.30HT
Matrix Comp. I Comp. I Comp. II
Comp. II
______________________________________
End Count
6.30 7.87 7.87 9.45
(ends/cm)
Nominal 0.762 0.584 0.584 0.457
Rivet (mm)
Cord dia-
0.838 0.686 0.686 0.610
meter (mm)
Cord 17 13 13 11
volume
content
(%)
Load
(MPa)
Critical
16.2 16.5 16.6 19.8
Gross 54.5 58.5 57.3 58.7
Strain (%)
Critical
-- 10.7 11.0 10.9
Gross -- 20.5 21.5 20.8
______________________________________
Table 1 values are based on the numerical average for 4 to 7 specimens
wherein the values of cord volume content are calculated from cross
sectional areas of reinforced cords, neglecting the space between the
filaments. The Table's values are further based on the preferred
embodiment illustrated herein of a 2 ply tire belt for radial passenger
tires with cords at opposing 23.degree. angles to each other. Table 1
illustrates a substantial improvement in the resistance to belt edge
separation initiation load which is the critical load for the composite
reinforced by 2x.30HT cord. For the 2x.30HT cord of the present invention
the critical load was 19.8 MPa while for 2+2x.25 and 2+7x.22 cords the
same load was well below 17 MPa. Note that the smaller diameter of the
2x.30HT cord permitted a higher end count of 9.45 ends per centimeter
within the limitation of good adhesion. It was further found that the end
count for 2x.30HT could be raised as high as 11.02 ends per centimeter
without loss of required rubber to cord adhesion due to the reduction in
river.
Initially cords of two twisted filaments of diameters of up to 0.38 mm
using conventional tire cord steel were tried which had large enough
diameters to give sufficient tensile strength of the cords but were found
to fail for lack of fatigue life of the composite. The new reinforcing
cords constructed from two high tensile steel wire filaments were found to
have an increase in fatigue life of the composite in addition to the
necessary tensile strength of the cord as illustrated in Table 2 and
filament diameters of less than 0.34 mm were found satisfactory for
meeting fatigue requirements.
TABLE 2
______________________________________
Tensile Fatigue Resistance of `Belt` Composites
in the Threshold Region
A B C
______________________________________
Reinforcement
2 + 2X.25 2 + 2X.25 2X.30HT
Matrix Comp. I Comp. II Comp. II
End count 7.87 7.87 9.45
(ends/cm)
Maximum Cyclic
16.9 16.9 16.9
Load (MPa)
(lb/in width)
# Cycles to 185,910 213,510 No damage at
failure 178,540 2,000,000 cycles
______________________________________
Note: The frequency of 10 cycles/sec is used.
Further for the same diameter and construction reinforcing cords made of
high tensile steel wire exhibited lower weight for equivalent modulus
values compared with those made of conventional steel wire for tire cord
of a lower carbon content. For example, the weight of 2+2x.25 high tensile
cord is 4% lower than that of 2+2x.25 cord of conventional steel for tire
cord.
For a given wire system two twisted filaments provide the lightest and
simplest cord construction which has the flexibility of a multi filament
cord. It has been determined that the use of a single filament of
sufficient diameter to provide the necessary tensile strength for a tire
belt reinforcement lacks the flexibility to give the necessary fatigue
life required for the belt composite.
It was experimentally observed that when the filament diameter of the
preferred embodiment cord, two filament cord, exceeded 0.34 mm Tabor
bending stiffness of the cord departs sharply from that of conventional
wire reinforcement with a similar cord diameter.
The above results suggest that a new metallic cord constructed from two
high tensile steel wire filaments with individual filament diameters of
less than 0.34 mm would be the preferred choice for belt reinforcement in
terms of bending stiffness and weight of the cord. More particularly,
2x.30HT cord becomes a direct substitute for 4x.25 or 2+2x.25 conventional
steel tire cord. While the 2x.30HT cord is a direct substitute it should
be noted that it has a lower weight and smaller cross sectional area
compared with 2x.30 conventional steel cord and 2+2x.25 cord respectively
(see Table 3).
TABLE 3
______________________________________
Relative Weight of Steel Cord Reinforcement
Construction Relative Weight
______________________________________
2x.30HT 88
2x.32HT 90
4x.25 94
2 + 2x.25HT 96
2 + 2x.25 100
2 + 2x.28HT 100
2 + 2x.28 104
2 + 7x.22 + 1 100
______________________________________
Note: The calculation of relative weight is based on the weight of wire
reinforcment and 1 mm thick rubber insulation on the top and bottom of th
wire.
It was also found that compared to conventional construction of similar
cord diameter for example 2+2x.25 the cut ends of two filament cord such
as 2x.30HT of the present invention are found to be more likely to
separate where they are cut often referred to as flara (see Table 4). This
increased tendency of filament separation at the cut ends of the cords can
result in an increased constraint over a local region of the rubber matrix
at a belt edge.
TABLE 4
______________________________________
Flare Length (mm) at 1 min after Cutting
2 + 2X.25 2X.30HT
(14 mm Lay Length)
(14 mm Lay Length)
______________________________________
8 0 17 10
0 5 5 5
8 0 20 3
8 5 5 6
7 0 14 11
10 5 5 6
5 10 10 7
2 6 5 6
2 7 3 4
8 7 8 5
Ave 5 Ave 8
______________________________________
Some of the more unexpected results of the belt package of the preferred
embodiment include a greater belt stiffness of 2 to 6% over the comparable
2+2x.25 cord reinforced belt package wherein usually a smaller diameter
cord in a belt of lighter weight would give less stiffness in a tire belt
reinforcement. Initial experimental data also indicates that the belt of
the preferred embodiment also gives better ride characteristics of the
tire while at the same time improving handling characteristics of the
tire. Ride is a quality associated with hoop stiffness and handling is
associated with the belt stiffness and while a softer ride usually is
obtained at the sacrifice of better handling, i.e., a stiffer belt, in the
present belt package both a softer ride and improved handling were
achieved.
Also it is observed that even at the preferred belt embodiment end count of
9.45 ends per centimeter in the smaller diameter cord there is a greater
plunger energy achieved over a comparable 2+2x.25 cord reinforced belt
which is a measure of resistance to penetration of a tire by foreign
objects.
While the preferred embodiment has been described herein as a two ply belt,
the present invention would also apply to belts for tires having more than
two plies as well as to other articles of multiple plies. As pointed out
about, even a single ply in accordance with the present invention would be
useful with conventional plies and further a single ply could well be
useful in tires or other articles as a single ply reinforcement. The
reinforcement of this invention is not limited to the particular
embodiment illustrated nor to necessarily the preferred two filament
embodiment, rather multi filament cords of a smaller diameter using high
tensile steel filaments having the characteristic high tensile modulus
coupled with the necessary flexibility for fatigue life and the stiffness
for lateral and planar support would also fall within the scope of this
invention.
In accordance with the provisions of the patent statutes, the principal and
mode of operation of the reinforced composite structure have been
explained and what is considered to represent its best embodiment has been
illustrated and described. It should, however, be understood that the
invention may be practiced otherwise than as specifically illustrated and
described without departing from its spirit or scope.
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